Means for producing waveforms for phase comparators as used in tv receivers and the like



Dec. 5, 1961 I. R. MORPHETT 3,012,201

MEANS FOR PRODUCING WAVEFORMS FOR PHASE COMPARATORS AS USED IN TVRECEIVERS AND THE LIKE Filed Sept. 28, 1959 INVENTOR IAN RIVERS MORPHETTBY I M M AGENT United States Patent M 3,012,201 MEANS FOR PRODUCINGWAVEFORMS FOR PHASE COMPARATORS AS USED IN TV RE- CEIVERS AND THE LIKEIan Rivers Morphett, Clarendon, South Australia, Australia, assignor toNorth American Philips Company, Inc., New York, N.Y., acorporation ofDelaware Filed Sept. 28, 1959, Ser. No. 842,834 3 Claims. (Cl. 328-134)This invention relates to phase comparators such as are used in TVreceivers for maintaining the correct phase relationship betweensynchronizing signals and a waveform produced by a cyclic waveformgenerator.

In such phase comparators it is common practice to compare thesynchronizing signals with a wave which is substantially of sawtoothform derived from the output of the generator by steps based upon theinitial addition of the synchronizing pulses to the steep sloping sidesof the sawtooth waveform, so that the peak voltage of the combinedwaveform is related to the phase difierence between the synchronizingsignals and the generated waveform. A control voltage can be derivedfrom this peak voltage. The precision and sensitivity of such a methodof phase comparison largely depends upon the steepness of the slope ofthe side of the sawtooth waveform, and the use of a sawtooth ensuresthat there is no danger of the generator locking incorrectly.

Alternatively, it is known to derive from the generated waveform aseries of pulses and by differentiating the latter to produce positiveand negative pulses of shorter duration and to add the synchronizingpulses to the sides of these pulses which are adjacent. These sides canbe made very steep and so a phase comparator based upon their use isboth sensitive and precise. However there is a danger that thesynchronizing pulses will fall on the flat portion of the waveform inwhich event the generator may lock out of synchronism.

It is also customary to apply the control voltage obtained by either ofthe methods described in the foregoing to an electrode of a valve whichcontrols the frequency and/ or phase of the generated cyclic waveform inseries with a DC. auxiliary voltage, so that the frequency or phase ofthe generated cyclic waveform may be varied at will be variation of thisauxiliary voltage.

The object of this invention is to provide a waveform which retains thesteepness of slope caused by differentiation and also diminishes thedanger of synchronization lock-out. This object is achieved by addingthe differentiated pulses derived from the pulses to a wave which issubstantially of sawtooth shape derived by integration from similarpulses of opposite polarity, thus providing a waveform particularlysuitable for use in a phase comparator.

In a preferred embodiment of the invention two sets of rectangularpulses of opposite polarity are derived from the scanning waveformgenerator of a television receiver, one set of these pulses is thendifferentiated while the other set is integrated to form a wave which issubstantially of sawtooth form and the resultants are added together toproduce a waveform basically of the sawtooth type, but with a sidehaving a very steep slope which is extended to produce peaks at thecorners of the substantially sawtooth waveform. Such a waveform iseminently suitable for addition to substantially rectangularsynchronizing pulses for the purpose of producing a control voltagerelated to the phase difference between the synchronizing pulses and thecyclic waveform.

The diagram of a typical circuit embodying the invention is depicted inthe single figure of the drawing. In the figure, T is a transformer inwhich a current of sawtooth waveform from the scanning waveformgenerator is flow- ICC Patented Dec. 5, 1961 2 ing in a winding S, whileS and S constitute a centretapped winding of the transformer, thecentre-tap being connected to ground so that at the outer terminalsrectangular voltage pulses of opposite polarity are produced,

such as indicated by the waveforms A and A shown in the figure. Thewaveform A is fed into an integrating circuit formed by a resistor R anda condenser C thus producing across the condenser C a wave which issubstantially of sawtooth form such as that depicted by the waveform BThe waveform is supplied to a differentiating circuit formed by acondenser C the resistor R and blocking condenser C and the condenser Cgthus producing a waveform by itself similar to that shown at B. Theblocking condenser C is not basically essential to the working of theinvention and may be omitted in suitable circuits. The two waveforms Band B are combined to produce the waveform C substantially of sawtoothshape with one side having a steep slope and with short pulses at thecorners of the sawtooth waveform. Voltage of this waveform C is appliedto the junction of the two diode rectifiers E and F connected in seriesand rectangular synchronizing pulses D and D of opposite polarity areapplied to the free terminals of the diodes E and F by two blockingcondensers C and C Two resistances R and R are connected across the twodiodes E and F and a condenser C is connected between ground and thejunction of the resistors R and R The control voltage produced by thisphase comparator is available across the terminals of the condenser C Aresistance R, is connected between the junction of the diodes E and Fand the adjustable contact on a potentiometer R and a second resistanceR from the junction of the resistors R and R to the same adjustablecontact on the potentiometer R provides a means for applying anauxiliary DC. voltage in series with the voltage produced by the phasecomparator.

In the figure the portion of the circuit shown which is in accordancewith the invention is the means for producing the waveform C and the useof this waveform is the phase comparator.

The embodiment of the invention described above is given by way ofexample only and other embodiments within the scope of the invention asdefined in the succeeding claims will occur readily to those skilled inthe art.

What is claimed is:

1. In a circuit for comparing the relative phases of synchronizingpulses and a deflection signal for producing a control voltage, meansfor deriving first and second rectangular pulses of opposite polarityfrom said deflection signal, means for integrating said first pulses,means for differentiating said second pulses, means combining saidintegrated first pulses and differentiated second pulses to produce avoltage waveform having a steeply sloping portion, and means forcomparing the phase of said combined first and second pulses with thephase of said synchronizing pulses.

2. A circuit for providing a control voltage dependent upon the relativephases of a train of synchronizing pulses and a current having asawtooth waveform comprising a transformer having a primary winding anda center-tapped secondary winding, means applying said current to saidprimary winding, means differentiating the voltage between one end andthe center tap of said secondary winding, means integrating the voltagebetween the other end and center tap of said secondary winding, meanscombining said integrated and differentiated voltages, and meanscomparing the phase of said combined voltage and the phase of saidsynchronizing pulses to produce said control voltage.

3. A circuit for providing a control voltage dependent upon the relativephases of a train of synchronizing pulses of said secondary winding,integrating capacitor means connected between said reference potentialand the junction of said resistors, means deriving a combined voltagefrom the junction of said difierentiating capacitor and differentiatingresistor, and means comparing the phase of said combined voltage and thephase of said synchronizing pulses to produce said control voltage.

References Cited in the file of this patent UNITED STATES PATENTS2,787,709 Janssen Apr. 2, 1957 2,795,733 Vilkomerson June 11, 19572,819,392 Thomas Jan. 7, 1958 2,855,542 Schade Oct. 7, 1958

